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Hardening effect and application of aluminum dihydrogen phosphate
The hardening mechanism of phosphate-bonded high alumina refractories is the result of chemical reaction of the phosphate binder with the material and adhesion cementation. The chemical reaction is due to the formation of aqueous aluminum dihydrogen phosphate, aluminum monohydrogen phosphate and their polymerization. When the orthophosphoric acid and the phosphate in the binder are completely neutralized, water-insoluble aluminum phosphate is formed, so that the material has strength.
The original or newly formed phosphate of different neutralization degree in the cement is initially in a colloidal state in the material, and a colloidal film of phosphate or orthophosphate is present on the surface of the material particles to adhere, but the strength is low. . During the drying process, the material is heated to lose physical water and some chemically bound water, increasing the concentration of phosphate. At the same time, during the heating process, the phosphate reacts with the oxide, and the aluminum dihydrogen phosphate is converted into aluminum monohydrogen phosphate, so that the material is converted into a chemical action by adhesion. Heating helps to create new compounds in the binder, and also improves the adhesion performance, the principle of curing aluminum dihydrogen phosphate, and the conversion of colloidal phosphate into crystalline, aluminum dihydrogen phosphate curing agent, therefore, The material strength is improved. As the heating temperature is increased, the strength is further improved due to the formation of a polymeric skeleton of the chain-like and cyclic tetrahedrons forming aluminum phosphate and aluminum oxide.
Phosphate-bonded high alumina refractories do not actually lose strength or heat loss at moderate temperatures (300-1000 C). This is because the chemically bound water is gradually lost, and the phosphate cementation is gradually replaced by ceramic bonding.
